Electronic mail (“email”) is a system and method for exchanging digital messages. Email systems employ a store-and-forward model in which email computer server systems accept, forward, deliver and store messages on behalf of users that connect to an email server, with a network-enabled device (e.g., a personal computer, a personal digital assistance (PDA), or the like) for the duration of message submission or retrieval. An email message consists of two components, the message header, and the message body, which is the email message's content. The message header contains control information, including an originator's email address and the email address of one or more recipients. Additional information can also be added to the header field, such as a subject of the email message. The body of the email can include a text message. The text can include encoded characters (e.g., hypertext) that can alter the formatting of the message as displayed to the user. Additionally, one or more files can be encoded into the body of the email message, which can be referred to as an attachment. By default, the body of an email message is unencrypted and transferred over an unsecured network, such as the Internet. Thus, an unauthorized user (e.g., a hacker) can intercept and access the email message.
Computer cryptography systems allow information to be encrypted and/or decrypted. As one example, information can be encrypted and decrypted with a symmetric cryptography key. In another example, information can be exchanged via a public/private key infrastructure (PKI). A PKI is an asymmetric (e.g., “one-way”) encryption scheme, wherein data encrypted by a public key can only be decrypted by a corresponding private key. In a PKI, a given entity's public key is freely distributed, while the private key is known only to the given entity. Information can be securely provided to the given entity by another entity when the another entity employs the public key of the given entity to encrypt information, and that information can only be decrypted with the private key of the given entity. In still another example, information can be exchanged via a double private key infrastructure. A double private key infrastructure is an asymmetric key structure wherein each first private key has a corresponding second private key, wherein information encrypted with the first private key can only be decrypted with the second private key, and vise-versa. However, in contrast to the PKI, in a double private key infrastructure, neither the first nor the second private key is freely distributed.